Currently a manufacturer of polyolefins, such as polyethylene, may test die swell characteristics of the polyolefin by producing a blow-molded product, such as a bottle, and then measuring the die swell. For example, the swell properties of a dairy grade polyethylene blow-molded bottle is measured by using a Uniloy blow-molding apparatus to prepare a bottle and then measuring the tab width, i.e., the flashing at the bottom of the bottle. The term “tab width” is synonymous with “die swell.” The processability of the polyolefin, as indicated by the swell analysis, is an important predictor of bottle quality. A polyolefin with too little swell will not properly fill the extremities of a mold, such as the handle of a bottle. A polyolefin with too much swell may form a molded article having flash in non-pinch-off areas and/or neck/tail flash which is difficult to trim. It is desirable to control swell in blow molding processes within acceptable limits.
Present methods of testing blow-molded articles, such as bottles, require large amounts, as much as 200 pounds, of polyolefin per batch and are labor intensive, time consuming and costly. There exists a need for a method of predicting die swell that reduces the labor, time, cost and amount of polyolefin tested per batch of polyolefin. There exists a need for a method of predicting, from one or more properties of the polyolefin, die swell of a polyolefin in a timely manner to permit modification of a polyolefin producing process to control the die swell of the polyolefin. There exists a need for a method of identifying and selecting polyolefins having predicted die swell within pre-selected ranges wherein the predicted die swell is based on rheological properties, other than die swell, of the polyolefin.
U.S. Pat. No. 4,603,173 discloses calculating flare swell percent and tube weight values for a polyolefin using a linear least squares fit method, but did not suggest or teach the use of partial least squares regression calculations for die swell correlation to other polyolefin properties.
U.S. Pat. No. 5,534,472 discloses the use of a Rheometrics Dynamic Analyzer RDA2 to measure dynamic storage modulus and loss modulus of certain ethylene-hexene copolymers prepared using a vanadium-containing catalyst and an aluminum containing co-catalyst, but did not suggest or teach the use of partial least squares regression calculations for die swell correlation to other polyolefin properties.
U.S. Pat. No. 6,479,597 B1 discloses the use of Raman spectroscopy to develop an equation for prediction hydrogen concentration in a polypropylene reactor using a regression analysis.
Additional references of interest include: U.S. Pat. Nos. 3,276,844; 3,321,280; 3,384,745; 4,003,712; 4,095,473; 4,341,891; 5,151,474; 5,624,877; 5,648,439; 5,671,591; 6,201,077 B1; 6,204,346 B1; 6,433,103 B1; 6,528,136 B1; 6,569,960 B2; and 6,610,799 B1.